1. Field of the Invention
This invention relates to an image judging device for judging quality of color reproduction, which is provided in a single-unit video camera-recorder, namely, a video camera or the like for achieving exact color reproduction. Further, this invention also relates to a color-chart discriminating device, a device for judging whether or not what is called a gray-world-assumption holds good for an input image (hereunder sometimes referred to as a GWA judgment device) and a device for deducing a light source, which are used for controlling a white balance control circuit. Furthermore, this invention also relates to a device for regulating color, which is used for achieving exact color reproduction.
2. Description of the Related Art
In recent years, with the spread of a video camera, means for following picture-taking conditions have become important more and more. Especially, it is very important for color reproduction to exactly deduce a light source used to take a picture. A means for deducing a light source by employing a plurality of photosensitive elements having different spectrum characteristics, as well as a means for deducing a light source by performing an image processing, has been well known as conventional source deducing means for deducing a light source. Lately, the latter source deducing means (hereunder sometimes referred to as AWB) has become mainly employed instead of the former source deducing means provided with the photosensitive elements, the design and costs of which are generally restricted.
The rationale of the technique of deducing a light source by performing an image processing (thus, the rationale of the AWB) is what is called Gray World Assumption (hereunder abbreviated as GWA), namely, an assumption that if colors of objects in a picture to be taken are mixed and thus averaged, an achromatic color (namely, a neutral color) is obtained as a resultant color. An example of a technique of regulating colors according to GWA is disclosed in the Japanese Unexamined Patent Publication (Kokal Tokkyo Koho) Official Gazette S56-36291. Further, the Japanese Unexamined Patent Publication Official Gazette H2-50592 discloses another example of the technique based on GWA and another assumption that a white part of a picture has high luminance.
However, the techniques based on GWA have a drawback in that frequently, a wrong light source is deduced and the balance of color in a picture is lost when GWA does not hold, for instance, in case where a part of a specific color has a large area in a picture. The present invention is created to eliminate such a drawback of the prior art.
It is, accordingly, an object of the present invention to an image judging device which can suitably regulate the balance of color in a picture even in case where a part of a specific color has a large area in the picture.
Such an image judging device, however, has encountered a problem that the image judging device judges that GWA does not hold good for a color chart often used to appraise an article of commerce and thus a deducing of a light source does not follow such a judgement even when an achromatic color is obtained as a result of mixing and averaging of colors of objects. This is due to the fact that generally, the variance (namely, the square of the standard deviation) of colors of a color chart in chromaticity space is extremely large. The present invention is accomplished to resolve such a problem encountered by the image judging device of the present invention.
It is, therefore, another object of the present invention to provide a color-chart discriminating device for discriminating a color chart from images of ordinary scenes.
Further, it is a further object of the present invention to provide an image judging device employing such a color-chart discriminating device.
Moreover, it is still another object of the present invention to provide a light-source deducing device employing such a color-chart discriminating device.
Furthermore, it is yet another object of the present invention to provide a light-source deducing device which can effectively deduce a light source in a picture even in case where a part of a specific color has a large area in the picture.
Additionally, it is a still further object of the present invention to provide a color regulating device employing such a light-source deducing device.